Changing the E-mail Notification Address

Hi, I have this small little issue regarding the e-mail address’s whenever someone receives and e-mail from my BBpress forum, or even when I receive an e-mail from my site regarding BBpress. Whenever someone signs up as a user on my forum, they get an email from username@box551.bluehost.com with their username and password. I have no idea why it’s from username@box551.bluehost.com, because my admin settings are set up for a different gmail account. I was on the phone with bluehost (my web hosting company) for a good hour and they tried everything they could and finally suggested that it was on BBPress’s end, and not theirs. So how would I change the default e-mail address to @gmail.com">username@gmail.com and not username@box551.bluehost.com when ever myself or a registered user to my BBpress forum receives an e-mail?